How to debug mavlink connections and messages

We have a research project in which we took over a system of PX4 FC (CUAV V5+) connected to a NUC and the NUC connected to some sensors we want to work with (mapping). There is also a GCS software for android that was written by our predecessors.

The idea is that the GCS starts a mission by communicating to the FC and throught the FC via MavLink also to the NUC.

Now actually we are having issues with this setup and basically it boils down to the question: “How can we debug MavLink connections?” In detail; how can we tap into the “network” and see what messages are send from/to devices? (We are working with directional messages no broadcasts.)

We looked into PX4 debug port and MavLink console. We also tryed wireshark etc. But none of these options allowed us to figure out what happens with the MavLink messages.